Furnace for and method of heating fluids



April 1937!- w. H. MINKEMA 2,076,856

FURNACE FOR AND METHOD OF HEATING FLUIDS Original Filed June 8, 1953,

I l I k o gfioooo-oo-oo-o- 4 ooo o-oo-oo-oo-o u' ll" Q Q Q -a INVENTORWILLIAM H. MINKEMA ATTORNEY Patented Apr. 13, 1937 PATENT OFFICE FURNACEFOR, AND

METHOD OF HEATING FLUIDS William H. Minkema,

Chicago, Ill., assignor to Universal Oil Products Company, Chicago,111., a corporation of Delaware Application June 8, 1933, Serial No.674,801

Renewed September 11, 1936 7 Claims.

This invention is particularly directed to the heating of fluids, suchas hydrocarbon oils, to the high temperatures required for theirpyrolytic conversion and is especially concerned with improvements to, atype of furnace designed for simultaneously subjecting equal streams ofthe same oil to equal heating conditions and with the method ofoperating such improved furnace.

The high charging capacities of modern cracking units has necessitatedthe design of furnaces to heat the large quantities of oil processed tothe high temperatures now commonly employed with a minimum pressuredrop, due to friction, through the heated fluid conduit withoutsacrificing their heating efliciency. The most successful method ofaccomplishing this, without excessively increasing the cross sectionalarea of the fluid conduit and thereby too greatly reducing the ratio ofheating surface to volume in the fluid conduit and thereby sacrificingheating efiiciency, has been to split the oil flowing through theheating coil into two or more equal streams, each of which aresimultaneously subjected to equal heating conditions in similar fluidconduits of the proper size, the separate streams being commingled atsome point within or subsequent to their passage through the fluidconduit and the comminglecl streams supplied to succeeding portions ofthe cracking system. The major difficulty encountered with such splitflow through theheating coil has been in obtaining equal heating of thedifferent streams and, more particularly, in arranging the heating coilor fluid conduit and so directing the flow of the separate streamstherethrough that equal heating conditions are obtained in the separatestreams. This is somewhat complicated by the fact that equal pressuredrop, due to friction, in the different streams is ordinarily dependedupon to maintain anequal volume of oil in the different streams. Thefriction encountered by the oil passing through the fluid conduit variesin direct relation to the volume of the oil at a given velocity or thevelocity of a given volume of oil and is, of course, directly affectedby the degree of vaporizationof the oil which in turn is dependent uponthe heating conditions to which it is subjected. It is thus apparentthat the heating conditions and the volume of oil flowing through theheating coil are inter-dependent and that the bad effects of unequalheating, in different parallel streams in fluid conduits connected attheir inlet and discharge ends, are accumulative.

- The present invention is concerned primarily ,55 with modern furnacesutilizing heating by both radiation and convection and employing highrates of heating, particularly in the radiant section of the furnace,and, for the purpose of illustration, we may consider a furnace having abank of tubes comprising a horizontal exposed row of horizontal tubesand a parallel shielded row of tubes located adjacent the roof of thefurnace and heated primarily by radiation from the combustion Zone and afluid heating bank W comprising horizontally parallel rows of horizontaltubes running at right angles to the direction of the radiant roof tubesand separated from the combustion zoneof the furnace by a bridge wall.In a furnace of this character equal heating of two separate streams ofoil may be obtained to a satisfactory degree in the fluid heating bankby, for example, dividing the bank vertically, in effect, into two bankscontaining an equal number of tubes and passing each stream successivelythrough half of the tubes in each successive horizontal row, the twostreams flowing in parallel and in the same direction through the twohalves of the entire bank. 'This same method of flow, however, asapplied to the radiant bank of roof tubes is satisfactory only whensubstantially identical heating conditions are maintained on oppositesides of the furnace. This is a diflicult condition to maintain since itis ordinarily necessary to employ a plurality of burners in largefurnaces of this character and slight variations in the adjustment ofdifferent burners as well as changes in the draft will materially changethe heating conditions in different portions of the furnace. Also eddycurrents set up by the combustion gases in the combustion zone, duetothe cooling effect of the tubes of the fluid conduit on the gases, areparticularly subject to change with slight changes in the firingconditions and draft and exert a marked influence upon the heatingconditions in different portions of the furnace.

In the present invention such changes in the firing conditions areprevented from upsetting equal heating conditions in the two streams bycausing the streams to cross fromthe exposed row of roof tubes to theshielded row of roof tubes at the middle of the radiant bank so thateach stream flows through the tubes in half of the exposed row andthrough the tubes in the opposite half of the shielded row. In thismanner different streams flow through the adjacent exposed row andshielded row on each side of the furnace and both streams are affectedby any change in the heating conditions on either side of the furnace.

The features of the present invention and the specific manner in whichequal heating of two equal streams of the same fluid is accomplished ina furnace of the type above described will be more apparent withreference to the accompanying diagrammatic drawing of such a furnace andthe following description thereof. It will be understood, however, thatthe features of the invention are not limited to use in the specificform of furnace illustrated and described but may be utilized toadvantage in many different types of furnaces and in its broad sense theI invention embraces any method and means of obtaining equal heating indifferent streams of the same fluid wherein the streams are caused tocross from one row to another of the fluid conduit in a mannersubstantially as herein disclosed.

Referring to the drawing, Fig. 1 is a cross sectional elevation of afurnace in which the features of the present invention are incorporatedand Fig. 2 is a longitudinal elevation shown in cross section of thesame furnace structure, the section being taken along a vertical planeindicated by the line 22 in Fig. 1.

The main furnace structure comprises side walls I and I, end walls 2 and2', a roof 3 and a floor 4. The interior of the furnace is divided 1 bymeans of a bridge wall 5 into a combustion and radiant heating zone 6and a fluid heating zone I. A bank 8 of horizontal tubes 9 which,

in the case illustrated, is divided into two similar banks 8' and 8" islocated in the fluid heating zone I of the furnace. The tubes of bank 8are arranged in a series of superimposed horizontal rows and each of thebanks 8' and 8" contain an equal number of tubes in the same row and thesame total number of tubes.

A radiant bank ll of horizontal tubes 9, comprising a shielded row I2and an exposed row l3 are located within the roof 3 of the furnace andparallel thereto. In accordance with the features of the presentinvention, the radiant bank ll of shielded and exposed roof tubes isdivided into two similar banks II and H"; bank II containing the tubesin the left hand half of exposed row 13 and the right hand half ofshielded row l2 while bank ll" contains the tubes in the right hand halfof exposed row I3 .and .the left hand half of shielded row l2. The twobanks II and H" contain an equal total number of tubes, each bankcontaining the same number of exposed tubes as the other bank and eachbank containing the same number of shielded tubes as the other bank.Also, there are an equal number of tubes in each of the banks H and II"on opposite sides of the furnace.

Combustibles of any desired form are supplied to the combustion zones 6of the furnace by means of suitable burners of any desired form (notshown) through firing ports such as indicated, for example, at H5 inFig. 2 located in wall 2 of the furnace. When desired, one or aplurality of checker walls such as indicated at [5 in Fig. 2, located atany desired point along the floor 4 of the furnace, may be utilized tobreak up the flame and assist combustion in the combustion zone. Thetubes 9 in roof bank H of the furnace are heated, primarily by directradiation from the flames and hot combustion gases in the combustionzone as well as reflected radiant heat from the hot refractory walls ofthe furnace. A minor amount of convection heat will ordinarily beimparted to the tubes in bank II from the hot combustion gases whichcome in contact therewith. The combustion gases from combustion zone 6of the furnace pass over the bridge wall 5 and downward through thefluid heating zone I to flue l6 and thence to a suitable stack (notshown). The tubes of bank 8, located within convection zone I, arethereby heated primarily by fluid heat from the hot combustion gasespassing from combustion zone 6 to flue l6, although some radiant heatmay be imparted to the tubes of this bank, particularly those in theupper rows.

The tubes 9 of both banks are connected in series at their ends by meansof suitable headers or return bends, located outside the heating zone,for example, such as indicated at ll in Fig. 2.

In accordance with the features of the present invention the fluidflowing through the heating coil is divided into two substantially equalstreams. The path of flow of the two streams through the fluid conduit,in the particular case here illustrated, is indicated in the drawing bythe single lines l8 and I8. The dotted portions of these lines betweentubes 9 indicates return bends I! on the far side of the furnace and thesolid portions of the lines between the tubes indicates return bends I"!on the near side of the furnace. The direction of flow of the fluid inthe two streams is indicated by the arrows. It will be noted, withreference to Fig. 1, that the two streams cross from the shielded row l2to the exposed row l3 at the middle of the radiant bank I I. By means ofthis arrangement both streams have an equal number of tubes on oppositesides of the furnace in radiant bank I l and both streams contain anequal number of exposed tubes and an equal number of shielded tubes.Also, the total number of tubes in one stream is equal to the totalnumber of tubes in the other stream. In this manner each stream isequally affected by any variation in the firing conditions on oppositesides of the furnace so that equal heating conditions are obtained inboth streams and thus with fluid of the same character supplied underuniform pressure to the inlet to the two parallel fluid conduitscomprising the two streams equal volumes of fluid will be dischargedfrom each coil at the same temperature.

I claim as my invention:

1. In heating hydrocarbon oils to conversion temperatures in a furnacehaving a fluid conduit comprising an exposed row and an adjacentshielded row of parallel tubes adjacent the roof of the furnace andabove a combustion zone therein and having means for supplyingcombustible fuel to the combustion zone through a plurality of burnersand in a general direction parallel to the tubes whereby to heat thetubes primarily by radiation, the improved method of securing uniformheating of two streams comprising equal quantities of the same oil whichcomprises passing the two streams, respectively, through the tubes inopposite halves of one row and then through the'tubes in the oppositehalf of the adjacent row whereby each stream is subjected to the heatingconditions prevailing on opposite sides of the combustion zone.

2. In a furnace for heating hydrocarbon oils to conversion temperatureshaving a fluid conduit comprising an exposed row and an adjacentshielded row of parallel tubes adjacent the roof of the furnace andabove a combustion zone therein, and means for supplying combustiblefuel to the combustion zone through a plurality of burners and in ageneral direction parallel to the tubes whereby to heat the tubesprimarily by radiation, so that two streams comprising equal quantitiesof the same hydrocarbon oil are uniformly heated, the combination ofmeans for conmeeting the tubes in opposite halves of each row in seriesand means for connecting the tubes in half of one row in series with thetubes in the opposite half of the adjacent row whereby each stream issubjected to the heating conditions prevailing on opposite sides of thecombustion zone.

3. In heating hydrocarbon oils to conversion temperature in a furnacehaving a fluid conduit comprising an exposed row and an adjacentshielded row of parallel tubes adjacent the roof of the furnace andabove a combustion zone therein and having means for supplyingcombustible fuel to the combustion zone through a plurality of burnerswhereby to heat the tubes primarily by radiation, the method ofuniformly heating two substantially equal streams of the oil whichcomprises passing each of the streams 530 in opposite directionssimultaneously through approximately half of the exposed row of tubesand through approximately half of the shielded row of tubes.

4. In heating hydrocarbon oils to conversion temperature in a furnacehaving a fluid conduit comprising an exposed row and an adjacentshielded row of parallel tubes adjacent the roof of the furnace andabove a combustion zone therein and having means for supplying com- 30bustible fuel to the combustion zone through a plurality of burnerswhereby to heat the tubes primarily by radiation, the method ofuniformly heating two substantially equal streams of the oil whichcomprises passing one of the streams 35 through approximately half ofthe shielded row of tubes and then through approximately half of theexposed row of tubes, and simultaneously passing the other stream in anopposite direction through the remaining portion of the shield- 40 edrow and then through the remaining portion of the exposed row of tubes.

5. In the heating of hydrocarbon oils to conversion temperatures in anexposed row and an adjacent shielded row of parallel heating tubes 45disposed in a combustion zone of a furnace having means for supplyingcombustible fuel to the combustion zone through a plurality of burnersand in a general direction parallel to the tubes whereby to heat thetubes primarily by radiation, the improved method of securing uniformheating of two streams comprising equal quantities of the same oil whichcomprises passing the two streams, respectively, through the tubes inopposite halves of one row and then through the tubes in the oppositehalf of the adjacent row whereby each stream is subjected to the heatingconditions prevailing on opposite sides of the combustion zone.

6. In the heating of hydrocarbon oils to conversion temperatures in anexposed row and an adjacent shielded row of parallel heating tubesdisposed in a combustion zone of a furnace having means for supplyingcombustible fuel to the combustion zone througha plurality of burnerswhereby to heat the tubes primarily by radiation, the method ofuniformly heating two substantially equal streams of the oil whichcomprises passing each of the streams 'in opposite directionssimultaneously through approximately half of the exposed row of tubesand through approximately half of the shielded row of tubes.

7. In the heating of hydrocarbon oils to conversion. temperatures in anexposed row and an adjacent shielded row of parallel heating tubesdisposed in a combustion zone of a furnace having means for supplyingcombustible fuel to the combustion zone through a plurality of burnerswhereby to heat the tubes primarily by radiation, the method ofuniformly heating two substantially equal streams of the oil whichcomprises passing one of the streams through approximately half of theshielded row of tubes and then through approximately half of the exposedrow of tubes, and simultaneously passing the other stream in an oppositedirection through the remaining portion of the shielded row and thenthrough the remaining portion of the exposed row of tubes.

WILLIAM H. MINKEMA.

